1. Field of the Invention
The present invention is directed to a plasma treatment device. In particular, the invention is directed to a plasma treatment device for a thin film formation process (plasma-assisted CVD and sputtering) or etch process utilizing the effect of plasma when manufacturing integrated circuits.
2. Description of the Related Art
An example of conventional plasma treatment devices will be described with reference to FIG. 12.
The plasma treatment device of FIG. 12 is a plasma-assisted CVD apparatus for forming silicon dioxide films. The device uses oxygen gas (O.sub.2) as a gaseous starting material for plasma generation and monosilane gas (SiH.sub.4) as a gaseous material for thin film formation. The silicon dioxide films produced are substantially the same as thermal oxidated films in terms of quality.
The plasma-assisted CVD apparatus shown in FIG. 12 is provided with a bell jar 11 used for plasma generation, a power-supplying mechanism 12 for supplying power to bell jar 11, a film-forming chamber 13 spatially connected to bell jar 11, a magnetic field generation mechanism 14 located around film-forming chamber 13 for forming a multicusp magnetic field therewithin, an evacuation mechanism 15 for evacuating bell jar 11 and chamber 13, a first gas-supplying mechanism 16 for supplying oxygen gas to chamber 13, and a second gas-supplying mechanism 17 for supplying the monosilane gas.
In this plasma-assisted CVD apparatus, bell jar 11, which is formed of a dielectric material, functions as a plasma generation chamber. More specifically, the upper end of bell jar 11, having a diameter of 100 mm when closed, is made of a quartz glass tube while the open lower end of the bell jar is connected to film-forming chamber 13. Power-supplying chamber 12 consists of a high frequency power source 21, a matching box 22, and a loop-shaped antenna 23 arranged around bell jar 11. High frequency power source 21 has a high frequency power of, for example, 13.56 MHz. However, a power source other than one limited to supplying high-frequency power could be used. Film-forming chamber 13 is formed of a cylindrical aluminum alloy and has, for example, a height of 230 mm and an inner diameter of 360 mm. Magnetic field generation mechanism 14 is arranged around film-forming chamber 13 and is formed of a rare-earth permanent magnet having 12 pairs of 24 poles. It is for the purpose of generating large-diameter and uniform plasma in film-forming chamber 13 that the multicusp magnetic field is formed therewithin by magnetic field generation mechanism 14.
Evacuation mechanism 15 consists of an evacuation chamber 31, two stage valves 32a and 32b, and an evacuation pump 33. The evacuation pump 33 has a turbo molecular pump 33a as the main evacuation pump and a dry pump 33b as a back-up evacuation pump.
Inside film-forming chamber 13 is a substrate holder 42 for supporting a substrate 41. Substrate holder 42 includes a structure 43, for circulating a thermo-exchanging medium, with a temperature detector therein (not shown in FIG. 12). Thus, substrate holder 42 is capable of controlling temperatures by heating or cooling to a specified temperature. A high-frequency power source 44 is connected to holder 42 so as to apply biased voltage to substrate 41. High-frequency power source 44 has a high frequency power of, for example, 400 kHz.
FIG. 13 is a sectional view along line A--A in FIG. 12. Outside the cylindrical wall part 13a of film-forming chamber 13 is a bar-shaped permanent magnet 51, having 12 pairs of 24 poles, arranged along the outer wall surface. The permanent magnet 51, having polarity of 12 pairs of 24 poles, is one of the components of the magnetic field generation mechanism 14. Magnet 51 is placed in parallel with the axial direction of the cylindrical wall part 13a. A pair of faces of magnet 51 is opposed to the outer wall surfaces of chamber 13 and is made of magnetic poles N and S, which are alternately arranged along the circumferential directions of the outer wall surfaces of chamber 13. A multicusp magnetic field 52 as shown in FIG. 13 is formed in the inner space of film-forming chamber 13 by magnet 51. Oxygen plasma coming into chamber 13 is difused along the configuration of the multicusp magnetic field 52 therein. The oxygen plasma is then brought into contact with the inner wall surface 13b of cylindrical wall part 13a of chamber 13 corresponding to the respective polar surfaces (N and S) of magnet 51 reflecting the configuration of the multicusp magnetic field 52.
As described above, the conventional plasma treatment device is constructed in such a way that the multicusp magnetic field 52 is generated in film-forming chamber 13 by means of the magnetic field generation mechanism 14 arranged around chamber 13. With the multicusp magnetic field 52, there are places 53 on surface 13b with which the oxygen plasma will come into contact and places 54 with which it will not. As a result, silicon dioxide thin films deposited on inner wall surface 13b may have differences in quality and thickness depending on the place on the inner wall surface where the film is formed. In other words, dense films, which are close to thermal oxidated films in quality, will be formed on the places 53 of inner wall surface 13b with which the oxygen plasma comes into contact since they receive charged particles from the plasma. On the other hand, as compared with places 53, rougher films will be formed on places 54 where the oxygen plasma does not come into contact. Consequently, using the conventional plasma treating devices will result in silicon dioxide films, having differences in density and in internal stress, being deposited and formed on inner wall surface 13b of film-forming chamber 13.
If silicon dioxide thin films continue to be deposited and formed on inner wall surface 13b of film-forming chamber 13 in the state described above, sooner or later, the thin films will peel off and fall from surface 13b due to the differences in internal stress. Peeling-off of the thin films will, in turn, cause generation of fine particulates which contaminate the substrate. When silicon dioxide thin films are formed on these contaminated substrates, many surface flaws or defects will be created leading to a deterioration in the quality of the thin films.